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Thursday, September 1, 2016

Was Lightning a Problem for Tall Dinosaurs?

The other day I came across this question and was shocked
that I hadn’t thought about it before.

Everyone knows lightning loves striking tall objects. Many
dinosaurs stood 15-20 feet tall, and big sauropods holding their necks
upright may have peered down on the world from 40 or 50 feet up! Were they
just giant walking lightning rods?

What a great question! Let’s break it down.

First of all...

Are tall objects
really more likely to be struck by lightning?

Yes, they are.

The (very short) life of a lightning strike goes like this:
the opposing charges between the cloud and the ground create paths of ionized
air called “step leaders.” These are basically hyper-conductive channels in the
air that gradually extend downward. When they reach the ground, or a grounded
object, the circuit is completed and a whole lot of charged particles move very
quickly along the path, creating a massive burst of electricity. Lightning.

(This
site explains it quite well, and in this video you can watch
it in slow motion! Look at those step leaders!)

As you’d imagine, tall objects, being closer to the clouds,
are more likely to be the first thing encountered by a descending step leader. So yes,
tall objects are at somewhat more risk of being hit by lightning. It’s not a definite,
though! Step leaders very often bypass
tall objects to strike the ground or shorter objects.

Do modern-day tall animals have lightning problems?

Many of the best tools in a paleontologist’s toolbox are
modern-day species. Giraffes and elephants are just as tall as many dinosaurs.
How do they fare when the storms come?

A quick internet search brings up lots of cases of animals
struck by lightning, including cows,
seals,
bison,
and more
cows, plus one from just the other day where over 300 reindeer were killed at once. Earlier this year, four
elephants in Sri Lanka were found dead after an apparent lightning strike,
and then there are the famous cases of the circus elephant and the Disney
World giraffe both struck and killed in front of witnesses.

In most of these cases, the animals are not struck directly,
but instead are caught near the
strike. This is not surprising, actually. According to NOAA, most cases of
humans hit by lightning happen when lightning jumps from a nearby taller object (this is why you shouldn't stand under a tree in a thunderstorm), or when the surge from the lightning spreads through the ground nearby (this is called ground current, and can be responsible for many deaths at once). This logically
would be the case for other animals, too.

In an interview
conducted after the lightning-death of a giraffe TV
star, experts commented (anecdotally) that giraffes don’t seem to be struck much more often than other animals. According to them, and another secondary report I’ve
read, giraffes have a habit of hiding under trees during storms, and sometimes
are killed when the tree is struck. Considering that most cases of lightning striking animals are indirect strikes, and that even for a giraffe there are taller objects around (like trees), it doesn't seem like big animals are really that much more at risk of being struck.So tall dinosaurs probably weren't lightning rods after all. But like modern animals, they certainly would have been at risk sometimes. So...

Could we find fossil
evidence of lightning-struck dinosaurs?

Right off the bat, I think we have plenty of evidence to
tell us if lightning was a problem for giant dinosaurs, and that’s the
diversity of giant dinosaurs. Huge sauropods were extremely numerous and widespread for more than 100 million
years. Clearly lightning was not enough of a problem to hold them back.

But dinosaurs must have
been struck by lightning on occasion – especially if standing under trees or
out in flat open fields. Would death-by-lightning be diagnosable in a fossil?

The effects of being struck by lightning are actually quite well-known.
Most of the time death is apparently caused by cardiac arrest as electricity disrupts
the heart. Lightning can also cause severe burning and tissue damage, and
survivors can suffer from problems with memory or cognition, even loss of hearing. This goes for humans as well as for other animals.

Problem is, cardiac arrest and memory problems don’t
fossilize. The important question is: does lightning damage bones? I dug around and
learned that fractures and dislocations may be caused by lightning, but they
are generally due to muscle spasms or blunt force trauma from the explosive
force of the strike, or from a fall after being thrown by the blast (see page 15
of this
PDF, and page 29 of this one).
Unfortunately, a paleontologist would probably have no way of knowing if a fracture in a fossil bone were caused by lightning as opposed to any number of other things.

But hey, what about skin? There are examples of fossilized dinosaur
skin, and lightning is known to leave morbidly beautiful ‘fractal
scarring.’ Do scars show up in fossils?

Actually, yes! One of the most famous dinosaur
specimens in the world, an Edmontosaurus named
“Dakota,” displays
really fantastic preservation of skin and muscle, and a 2013
study found a tiny patch of skin where the normal scale pattern was
disrupted – an ancient scar! So yes, it may actually be possible to find a
lightning-scarred dinosaur. Wouldn't that be cool?Of course, given how rare fossilized skin is, how
rarely animals are struck by lightning, and how rarely dead dinos are
fossilized in the first place, odds aren’t good that we'll find a fractal-scarred dinosaur anytime soon. But you never know...

Just like modern animals (including people!) dinosaurs would have occasionally foundthemselves in an open area or near a tree during a storm, and may have been victims of lightning,as imagined in this fantastically appropriate recreation, used with permission from the artist.

3 comments:

I may be wrong, but I believe that the effects of the ground current are likely worse for large sauropods than they are for, say, giraffes. This because the danger of ground currents stem from the voltage difference between your feet - the further your feet are apart, the larger the voltage difference when a strike to the ground occurs; and the bigger the voltage difference, the larger the current flowing through your body. This is why people tell you to keep your feet close together when there is a risk lightning may strike near you. Cows are often used as an example - their front and hind legs are quite far apart, so many cows die from ground currents. The big sauropods you talk about have a pretty large distance between from and hind legs... http://www.lightningsafety.noaa.gov/science/science_ground_currents.htm

With that in mind, even if sauropods weren't more likely to be struck directly, ground current may have been more deadly to them than smaller animals. Although I wonder if there's a point where it doesn't matter anymore. If a cow's legs are already far enough apart to be often deadly, maybe a sauropod is just overkill (so to speak).